Transparent displays are long sought-after by scientists and engineers. Two-dimensional (2D) transparent displays can create images that appear floating in the air, in contrast to traditional displays where images appear on a visible screen. Aside from creating special visual impressions, such displays can have a wide variety of applications. A glass window can be turned into the screen of a home theater. Eyeglasses can become a mini computer screen. The windshield of a vehicle can show information such as maps without blocking the driver's view. The display window of a store can show not only products but also their information.
A number of transparent display technologies exist, but none have gained a widespread usage. Liquid crystal displays (LCD) can be made transparent by eliminating the backlight, but they are not very transparent (the typical transmittance may be less than 15%). Organic light-emitting diodes (OLEDs) can also be made transparent, but the production remains costly and the transmittance is also limited (typically less than 40%). OLED displays can be made flexible and foldable, so transparent flexible displays are also possible. Electroluminescent displays have also been made transparent, but have so far been limited to single colors. Recently, fluorescent films have been combined with ultraviolet (UV) lights to make multi-colored displays that are transparent; however, an intense UV light source, such as an ultra high performance (UHP) lamp, is required due to the small emission cross sections of the fluorescent particles.